This invention relates to a liquid ejecting apparatus for ejecting liquid pressurized in pressure generating chambers in the form of liquid drops through nozzle orifices.
There is known a liquid ejecting device of the type which ejects a liquid pressurized in a pressure generating chamber in the form of liquid drops through nozzle orifices, and the liquid ejecting apparatus is capable of ejecting any of various kinds of liquids. A typical example of such a liquid ejecting device is a recording head used in an ink jet recording apparatus. A related technique will be discussed with reference to FIGS. 8 and 9 by taking a record head of an ink jet record apparatus as an example.
The recording head includes a flow passage unit 1 having nozzle orifices 2 and a head case 9 in which the flow passage unit 1 is attached thereto by bonding.
The flow passage unit 1 is formed with a nozzle plate 3, a passage substrate 5 and a vibration plate 6, which are laminated into a unit form. The nozzle plate 3 has a nozzle forming surface 3A in which an array of nozzle orifices 2 are formed. The passage substrate 5 includes an array of pressure generating chambers 4 formed therein which respectively communicate with the nozzle orifices. The vibration plate 6 closes the openings of lower parts of the pressure generating chambers 4. Ink reservoirs 8 are formed in the passage substrate 5. Each ink reservoir 8 communicates with the pressure generating chamber 4 associated therewith via an ink passage 7, and reserves ink to be fed to the pressure generating chamber 4. The whole recording head is denoted as H.
The head case 9, which forms a base member of the recording head H, is formed by injection molding using thermosetting resin or thermoplastic resin. A pressure generating element 11 is placed in a space 10 which vertically extends in the structure. A back end of the pressure generating element 11 is fixed to a fixing plate 12 mounted on the head case 9, and a fore end of the same is fixed to a island 6A on the lower surface of the vibration plate 6.
A pressure generating chamber 4, a pressure generating element 11, and a nozzle orifice 2 are vertically arranged in the structure. A number of combinations each consisting of them are arrayed in a direction perpendicular to a surface of the drawing. In this instance, two linear arrays of nozzle orifices are formed. Those nozzle linear arrays eject ink such that the same kind of ink is ejected for each nozzle linear array.
Conducting wires for input 13 are connected to the pressure generating elements 11, respectively. The conducting wires are inserted into and passed through through-holes 14A of a head substrate 14, and then connected to printed wirings 15 on the head substrate 14. The printed wirings 15 are gathered and connected to a flexible flat cable 17 via a connector 16. The flexible flat cable 17 is connected to a drive circuit (not shown). When a drive signal is input from the drive circuit to the pressure generating element 11, the pressure generating element 11 is expanded and contracted in the longitudinal direction to vary a pressure within the pressure generating chamber 4. Then, the ink within the pressure generating chamber 4 is ejected through the nozzle orifices 2 in the form of ink drops.
A damper recess 18 is formed at a part of the head case 9 corresponding to each ink reservoir 8. When ink is ejected, the damper recess damps a pressure variation in the ink reservoir 8 with the aid of the vibration plate 6 formed with a polyphenylene sulfide film (referred to as a PPS film). The damper recess 18 is a space isolated from exterior. Air in the damper recess 18 flows out into the ink so as to permeate through the vibration plate 6 formed with the PPS film. An air pressure in the damper recess 18 decreases, and a tension of the vibration plate 6 becomes high. As a result, an unsatisfactory damping effect is frequently obtained. To cope with this, a communication passage 19, which enables the damper recess 18 to communicate with the air, is provided extending from the bottom surface of the damper recess 18 to the opposite surface of the head case 9, to thereby prevent the pressure reduction within the damper recess 18.
In the above structure, an opening area of the damper recess 18 is large, and hence, an area of the vibration plate 6, which covers the opening area, is also large. In particular, when the ink jet recording apparatus is put in a nonuse state, the water content of the ink evaporates and permeates through the vibration plate 6 having the large opening area, and flows into the damper recess 18. With its pressure increase, the vapor passes through the communication passage 19 and scatters into the air. In such a phenomenon, the amount of water in the ink decreases and a viscosity of ink increases. As a result, when the ink jet recording apparatus is operated again, the ink drop ejection is improper. To avoid this, a passage resistance of the communication passage 19 is increased to thereby prevent the excessive vaporation of the water content of the ink.
The ink jet recording apparatus designed for the color printing uses plural kinds of color inks of yellow, magenta, cyan and the like, in addition to black ink. Further, nozzle orifices 2 are provided which are respectively assigned for those colors.
When the print data terminates and the recording head H is put in a non-use state, ink presented at a vicinity of the nozzle orifices 2 is dried, so that the nozzle orifices will be clogged with the dried ink. For this reason, in the related technique, the recording head H is sealed with the cap 38 when no printing operation is performed. The cap 38 is coupled to a suction pump 39 for performing a cleaning operation described below. When the recording head is left in a sealed state for a long time, a solvent of the ink presented at the vicinity of the nozzle orifices 2 gradually evaporates and a viscosity of the ink increases. In a state that the viscosity of the ink is increased, some troubles tend to occur. For example, the printing operation cannot start quickly or a print quality is deteriorated. The nozzle orifices 2, which continuously ejects ink drops in the printing operation, successively receive new ink, and little suffers from the clogging. In the case of the nozzle orifices 2, which are located, for example, at the upper and lower ends of the nozzle array, and have each an extremely small chance of ejecting ink drops, the ink located near those nozzle orifices 2 dries during the printing operation and its viscosity increases, and the recording head is likely to be clogged with the dried ink.
To cope with such a problem, a “flushing operation” or “cleaning operation” is performed for one form of a preparatory operation before the printing operation starts. In the preparatory operation, at a time point that power to the recording apparatus is turned on or that a print signal is first input to the recording apparatus, the nozzle orifices 2 are forcibly caused to eject ink drops independently of the printing, whereby the clogging is removed and the ink ejection ability of the recording head is recovered.
The “flushing operation” removes the ink having an increased viscosity presented at the vicinity of the nozzle orifices 2 in a manner that a drive signal is applied to the pressure generating element 11 independently of print data, and the recording head is caused to eject ink drops of such an ink. The “cleaning operation” is performed when the clogging of the nozzle orifices 2 is not removed completely by only “the flushing operation. In the “cleaning operation”, a negative pressure is applied to the nozzle orifices 2 by use of a suction pump thereby to forcibly suck the ink of the increased viscosity in the pressure generating chambers 4 and others.
The viscosity of the ink presented at the vicinity of the nozzle orifices 2 is more increased and the clogging of the nozzle orifices 2 is more deteriorated as a time (cap leaving time) that the recording head H is left as it is sealed with the cap and a total printing time till the recording head is sealed with the cap are longer. Which of the “flushing operation” and the “cleaning operation” is to be performed is determined by a relation (correlation) between the cap leaving time and the total printing time as shown in FIG. 9. When the cap leaving time or the total printing time is short (in a flushing area indicated by FL1 to FL4 ), the flushing operations are performed. When the cap leaving time or the total printing time is long (in the cleaning area), the cleaning operation is performed.
As shown in FIG. 9, the flushing area that is determined by a relation (correlation) between the cap leaving time and the total printing time, is defined into four areas (FL1 to FL4 in this instance) depending on a level of viscosity increase of the ink at and near the nozzle orifices 2. In the area FL1, a degree of the viscosity increase of the ink at and near the nozzle orifices 2 is the lowest. In this degree, to recover the ink ejection ability of the nozzle orifices 2, the black ink (BK) is ejected by 100 shots, and the color ink (COL) is ejected by a small number of shots, 50 shots.
When the cap leaving time or the printing time is somewhat longer than that in the flushing area FL1, the increase degree of the ink at and near the nozzle orifices 2 somewhat increases from that in the flushing area FL1. Therefore, the recovering operation is performed in a flushing area FL2. To recover the ink ejection ability of the nozzle orifices 2, the black ink BK is ejected by 1000 shots, and the color ink COL is ejected by 500 shots, larger than in the flushing area FL1.
In this way, the recovering area is stepwise shifted and finally a flushing area FL4 is reached in which the ink viscosity increase degree is the highest. In this flushing area, the black ink BK is ejected by 5000 shots, and the color ink COL is ejected by 3000 shots to thereby recover the ink ejection ability of the nozzle orifices.
The recovering operations are performed before an operation job is executed. The operation job consists of an ink ejection operation of the recording head H, which ranges from an instant that the recording head H starts an ink ejection in response to an operation command signal applied thereto till the recording head ends the ink ejection. In a specific example where the recording head receives a one-operation command signal, which instructs a print of a letter of 3 pages and starts an ink ejection for printing the letter, an operation of the recording head ranging from the start to the end of the ink injection forms one operation job. The recovering operation in any of the recovering areas is performed before the operation job. In another example where another operation command signal to print a short sentence of about 5 lines after the printing of the letter ends is applied, for another operation job, to the recording head H, the recovering operation in any of the recovering operation areas is performed before the printing operation of the short sentence starts.
When the recovering operation of the recording head shifts from the flushing operation defined by the areas FL1 to FL4 to the cleaning operation, the cleaning operation is performed before the operation job starts. By the cleaning operation, the ink having the considerably increased viscosity is forcibly sucked from the nozzle orifices 2 of the recording head, to thereby recover the normal ink ejection ability of the recording head. After the cleaning operation is performed, a state of the ink at and near the nozzle orifices 2 is returned to a state substantially equal to the initial state that the ink having increased viscosity is removed. Then, the cap leaving time or the printing time is reset, and both the times are counted again from the start.
Although the flushing operation is performed in response to the viscosity increase degree as described above, such consideration is not given to the cleaning operation performed following the flushing operation. Also, consideration is not given either to the point in which some operation condition in the flushing operation is intentionally selected and the cleaning operation is performed depending on the selected operation condition.